Glasshouse and field experiments were conducted in 1993 at the
International Livestock Research
Institute (ILRI) in Addis Ababa to identify effective combinations of
Trifolium semipilosum
genotypes and Rhizobium leguminosarum bv. trifolii strains
and to investigate the effects of
waterlogging of Vertisols on the response of clover to inoculation. In
the
glasshouse, the Rhizobium
strain ILCA372str produced nearly ten times as much nodule DM, three times
as
much shoot DM,
five times as much root DM, and twice as much plant N on cv. Safari as
it
did on accession ILCA7609
under normal watering conditions. This spontaneous streptomycin-resistant
mutant strain performed
better than its parent strain. Shoot DM and N yields of this combination
were,
however, only 55 and 71%, respectively, of the corresponding N-fertilizer
(150 kg N ha−1) treatment. Waterlogging
reduced nodule DM by 33%, shoot DM by 41%, root DM by 25% and N yield by
33%, and
responses of both plant genotypes to inoculation and to N fertilizer were
reduced. In the field, there
were no significant differences in nodulation, plant DM and plant N between
seed and soil inoculation methods. Dry matter and N yields of Safari inoculated
with
strain ILCA372str were at
least twice as high as those produced by any other strain or N fertilizer
supplied at 100 kg N ha−1.
Waterlogging during early establishment in the field probably reduced
the availability of N fertilizer
to the plants. Further field testing of the Safari-ILCA372str combination
is recommended, particularly in combination with broad-bed and furrow
(BBF) technology to drain Vertisols.